In the exploration of oil, gas and geothermal energy, drilling operations are used to create boreholes, or wells, in the earth. Subterranean drilling necessarily involves the movement of long lengths of tubular sections of pipe. At various intervals in the drilling operation, all of the drill pipe must be removed from the wellbore. This most commonly occurs when a drill bit wears out, requiring a new drill bit to be located at the end of the drill string. It can also be necessary to reconfigure the bottom-hole assembly or replace other downhole equipment that has otherwise failed. When the drill pipe has to be removed, it is disconnected at every second or third connection, depending on the height of the mast. On smaller drilling rigs used in shallower drilling, every other connection is disconnected, and two lengths of drill pipe, known as “doubles” are lifted off of the drill string, aligned in the fingers of the rack by the derrickman, and then lowered onto the drill floor away from the well center. On larger drilling rigs used for deeper drilling, every third connection is disconnected and three lengths of drill pipe, known as “triples” are lifted off of the drill string, aligned in the fingers of the rack by the derrickman, and then lowered onto the drill floor away from the well center. The doubles and triples are called a stand of pipe. The stands are stored vertically on the rig floor, aligned neatly between the fingers of the rack on the mast.
Removing all of the drill pipe from the well and then reconnecting it to run back into the well is known as “tripping the pipe” or “making a trip,” since the drill bit is making a round trip from the bottom of the hole to the surface and then back to the bottom of the hole. Tripping the drill pipe is a very expensive and dangerous operation for a drilling rig. Most injuries that occur on a drilling rig are related to tripping the pipe. Additionally, the wellbore is making no progress while the pipe is being tripped, so it is downtime that is undesirable. This is why quality drill bits are critical to a successful drill bit operation. Drill bits that fail prematurely can add significant cost to a drilling operation. Since tripping pipe is “non-drilling time,” it is desirable to complete the trip as quickly as possible. Most crews are expected to move the pipe as quickly as possible. The pipe stands are long and thin (about ninety feet long).
There are a number of variables that contribute to irregular and hostile movement of the pipe stand as it is disconnected and moved to the rack for setting on the drill floor, as well as when it is being picked up for alignment over the wellbore center for stabbing and connection to the drill string in the wellbore. For example, the vertical alignment and travel of the elevator and hoist connection which lift the drill string from the wellbore is cable connected, and capable of lateral movement which is translated to the drill string rising from the wellbore. Also, the drill string is supported from the top, and as the derrickman moves the drill string laterally, the accelerated lateral movement of the long length of the pipe stand away from the well center generates a wave form movement in the pipe itself. As a result of the natural and hostile movement of the heavy drill stand, which typically weighs between 1,500 and 2,000 lbs., and drill collars which weigh up to 20,000 lbs., it is necessary for crew members to stabilize the drill pipe manually by physically wrestling the pipe into position. The activity also requires experienced and coordinated movement between the driller operating the drawworks and the derrickman and floorhands. Needless to say, many things can and do go wrong in this process, which is why tripping pipe and pipe racking is a primary safety issue in a drilling operation.
Attempts have been made to mechanize all or part of the pipe racking operation. On offshore platforms, where funding is justifiable and where drill floor space is available, large Cartesian racking systems have been employed, in which the pipe stands are gripped at upper and lower positions to add stabilization, and tracked modules at the top and bottom of the pipe stand coordinate the movement of the pipe stand from the wellbore center to a racked position. Such systems are very large and very expensive, and are not suitable for use on a traditional land based drilling rig.
A previous attempt to mechanize pipe racking on conventional land based drilling rigs is known as the Iron Derrickman® pipe-handling system. The apparatus is attached high in the mast, at the rack board, and relies on a system of hydraulics to lift and move stands of drill pipe and collars from the hole center to programmed coordinates in the racking board. This cantilever mast mounted system has a relatively low vertical load limit, and therefore requires assistance of the top drive when handling larger diameter collars and heavy weight collars.
The movement of the pipe with this system is somewhat unpredictable and requires significant experience to control. It grasps the pipe from above the center of gravity of the tubular and fails to control the hostile movement of the pipe stand sufficiently to allow for safe handling of the stands or for timely movement without the intervention of drilling crew members. In particular, the system is not capable for aligning the lower free end of the drill stand accurately for stabbing into the drill string in the wellbore. As a result of these and other deficiencies, the system has had limited acceptance in the drilling industry.
An alternative system that is known provides vertical lifting capacity from the top drive and a lateral movement only guidance system located near the rack. The system still requires a floorman for stabbing the pipe to the stump as well as to the set-back position.
A primary difficulty in mechanizing pipe stand racking is the hostile movement of the pipe that is generated by stored energy in the stand, misaligned vertical movement, and the lateral acceleration and resultant bending and oscillation of the pipe, which combine to generate hostile and often unpredictable movements of the pipe, making it hard to position, and extremely difficult to stab.
A conflicting difficulty in mechanizing pipe stand racking is the need to move the pipe with sufficient rapidity that cost savings are obtained over the cost of manual manipulation by an experienced drilling crew. The greater accelerations required for rapid movement store greater amounts of energy in the pipe stand, and greater attenuated movement of the stand.
Another primary obstacle in mechanizing pipe stand racking is the prediction and controlled management of the pipe stand movement sufficient to permit the precise alignment required for stabbing the pipe to a first target location on the drill floor and to a second target location within the fingers of the racking board.
An even greater obstacle in mechanizing pipe stand racking is the prediction and controlled management of the pipe stand movement sufficient to achieve the precise alignment required for stabbing the tool joint of the tubular held by the racking mechanism into the receiving tubular tool joint connection extending above the wellbore and drill floor.
Another obstacle to land-based mechanizing pipe stand racking is the lack of drilling floor space to accommodate a railed system like those that can be used on large offshore drilling rigs.
Another obstacle to mechanizing pipe stand racking is the several structural constraints that are presented by the thousands of existing conventional drilling rigs, where the need to retrofit is constrained to available space and structure. For example, existing structures require orthogonal movement of the drill stand over a significant distance and along narrow pathways for movement.
Another obstacle to mechanizing pipe stand racking is the need to provide a reliable mechanized solution that is also affordable for retrofit to a conventional drilling rig. Still another obstacle to mechanizing pipe stand racking is the need to grip and lift pipe stands within the narrow confines of parallel rows of pipe stands in a conventional rack.
It is also desirable to minimize accessory structure and equipment, particularly structure and equipment that may interfere with transportation or with manpower movement and access to the rig floor during drilling operations. It is further desirable to ergonomically limit the manpower interactions with rig components during rig-up for cost, safety and convenience.
Thus, technological and economic barriers have prevented the development of a pipe racking system capable of achieving these goals. Conventional prior art drilling rig configurations remain manpower and equipment intensive to trip pipe and rack pipe when tripping. Alternative designs have failed to meet the economic and reliability requirements necessary to achieve commercial application. In particular, prior art designs fail to control the natural attenuation of the pipe and fail to position the pipe with sufficient rapidity and accuracy.
A goal of the racker invention is to achieve rapid and accurate unmanned movement of the pipe between the racked position and the over-well position. Thus, the racker must avoid storage of energy within the positioning structure. True verticality is critical to limiting the energy storage of the system. Additionally, controlled movement and positional holding of the stand is critical to allowing rapid movement by adding the stiffness to the system.
In summary, the various embodiments of the present invention provide a unique solution to the problems arising from a series of overlapping design constraints, including limited drill floor space, and obtaining sufficient stiffness from a retrofittable assembly to provide a controlled and precise automated movement and racking of drill pipe. More specifically, the various embodiments of the present invention provide for lateral movement of the pipe stand independent of assistance from the top drive, and without extension and retraction of the top drive for handing the pipe stand to the racking system. This provides free time for the top drive to move with the racker system in positioning the pipe without assistance from the top drive. Additionally, the various embodiments of the present invention provide a device capable of precise and accurate stabbing of the drill stand, resulting in faster trip time.